Systems and methods for estimating a tag&#39;s location

ABSTRACT

Systems ( 100 ) and methods for determining a location of a tag ( 310 ). The methods involve: receiving, at each detector of a plurality of detectors ( 202 - 216, 306, 308 ), a device transmission periodically transmitted from the tag; determining, by the detectors, Received Signal Strength Indictors (“RSSIs”) for the device transmission received thereat; determining, by a computing device ( 218 ), a probable location of the tag within the passage, first demarcated area or second demarcated area using the RSSIs and relationships between the RSSIs; determining a first likelihood value indicating the likelihood that the probable location is correct; and determining an estimated location of the tag within the passage, first demarcated area or second demarcated area based on the probable location when the first likelihood value meets a first criteria.

FIELD OF THE INVENTION

This document relates generally to wireless based systems. Moreparticularly, this document relates to systems and methods fordetermining Received Signal Strength Indicator (“RSSI”) based locationprofiles of tags.

BACKGROUND OF THE INVENTION

Electronic Article Surveillance (“EAS”) systems are often used by retailstores in order to minimize loss due to theft. One common way tominimize retail theft is to attach a security tag to an article suchthat an unauthorized removal of the article can be detected. In somescenarios, a visual or audible alarm is generated based on suchdetection. For example, a security tag with an EAS element (e.g., anacousto-magnetic element) can be attached to an article offered for saleby a retail store. An EAS interrogation signal is transmitted at theentrance and/or exit of the retail store (“the interrogation zone”). TheEAS interrogation signal causes the EAS element of the security tag toproduce a detectable response if an attempt is made to remove thearticle without first detaching the security tag therefrom. The securitytag must be detached from the article upon purchase thereof in order toprevent the visual or audible alarm from being generated.

One type of EAS security tag can include a tag body which engages atack. The tack usually includes a tack head and a sharpened pinextending from the tack head. In use, the pin is inserted through thearticle to be protected. The shank or lower part of the pin is thenlocked within a cooperating aperture formed through the housing of thetag body. In some scenarios, the tag body may contain a Radio FrequencyIdentification (“RFID”) element or label. The RFID element can beinterrogated by an RFID reader to obtain RFID data therefrom.

There are many known algorithms for determining the distance between atag and another device or object (e.g., a tag reader or an EAS systempedestal defining an interrogation). One such algorithm is based onReceived Signal Strength Indicator (“RSSI”) information. This RSSI basedalgorithm is hindered by the uncertainty of factors affecting thereceived signal strength such as loading of the antenna and the spatialorientation of one antenna to another antenna. In a passage system, itis desirable to quickly identify the presence of an EAS devicecontaining an identification code within the interrogation zone.However, the scattering of Radio Frequency (“RF”) signals, loadingeffects, and spatial relation of one antenna to another introducesuncertainties as to the true location of the device.

SUMMARY OF THE INVENTION

The present disclosure concerns implementing systems and methods fordetermining a location of a tag. The methods involve receiving, at eachdetector of at least one of a plurality of first detectors and aplurality of second detectors, a device transmission periodicallytransmitted from the tag. The plurality of first detectors is disposedin proximity to a passage at which a person can transition from a firstdemarcated area to a second demarcated area. The plurality of seconddetectors is disposed within the first and second demarcated areas. Thepassage is sub-divided into a plurality of zones.

Next, the plurality of first detectors and/or the plurality of seconddetectors determine Received Signal Strength Indictors (“RSSIs”) for thedevice transmission received thereat. The RSSIs and the relationshipstherebetween are used to determine a probable location of the tag withinthe passage, first demarcated area or second demarcated area. A firstlikelihood value is determined that indicates the likelihood that theprobable location is correct. An estimated location of the tag withinthe passage, first demarcated area or second demarcated area is thendetermined based on the probable location when the first likelihoodvalue meets a first criteria.

The estimated location comprises a zone selected from the plurality ofzones where the device transmission originated. The zone is selectedbased on relational RSSI ratios computed using the RSSIs determined bythe plurality of first detectors.

DESCRIPTION OF THE DRAWINGS

Embodiments will be described with reference to the following drawingfigures, in which like numerals represent like items throughout thefigures, and in which:

FIG. 1 is an illustration of an exemplary passage that is useful forunderstanding the present invention.

FIG. 2 is an illustration of an exemplary passage having a plurality ofdetectors disposed on or adjacent thereto.

FIG. 3 is an illustration of an exemplary retail store facility in whichthe passage of FIGS. 1-2 is employed.

FIG. 4 is a functional block diagram of the passage algorithm employedby the computing device of FIG. 2.

FIG. 5 is a block diagram of an exemplary architecture for a detector.

FIG. 6 is a block diagram of an exemplary architecture for a computingdevice.

DETAILED DESCRIPTION OF THE INVENTION

It will be readily understood that the components of the embodiments asgenerally described herein and illustrated in the appended figures couldbe arranged and designed in a wide variety of different configurations.Thus, the following more detailed description of various embodiments, asrepresented in the figures, is not intended to limit the scope of thepresent disclosure, but is merely representative of various embodiments.While the various aspects of the embodiments are presented in drawings,the drawings are not necessarily drawn to scale unless specificallyindicated.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by this detailed description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

Reference throughout this specification to features, advantages, orsimilar language does not imply that all of the features and advantagesthat may be realized with the present invention should be or are in anysingle embodiment of the invention. Rather, language referring to thefeatures and advantages is understood to mean that a specific feature,advantage, or characteristic described in connection with an embodimentis included in at least one embodiment of the present invention. Thus,discussions of the features and advantages, and similar language,throughout the specification may, but do not necessarily, refer to thesame embodiment.

Furthermore, the described features, advantages and characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. One skilled in the relevant art will recognize, in light ofthe description herein, that the invention can be practiced without oneor more of the specific features or advantages of a particularembodiment. In other instances, additional features and advantages maybe recognized in certain embodiments that may not be present in allembodiments of the invention.

Reference throughout this specification to “one embodiment”, “anembodiment”, or similar language means that a particular feature,structure, or characteristic described in connection with the indicatedembodiment is included in at least one embodiment of the presentinvention. Thus, the phrases “in one embodiment”, “in an embodiment”,and similar language throughout this specification may, but do notnecessarily, all refer to the same embodiment.

As used in this document, the singular form “a”, “an”, and “the” includeplural references unless the context clearly dictates otherwise. Unlessdefined otherwise, all technical and scientific terms used herein havethe same meanings as commonly understood by one of ordinary skill in theart. As used in this document, the term “comprising” means “including,but not limited to”.

In the present disclosure, there are described systems and methods forimproving detection accuracy with Received Signal Strength Indicator(“RSSI”). The methods involve estimating a tag's position by combiningmultiple received RSSI signals. Each RSSI signal may be received from atag or other transmitting device. Therefore, the transmission isreferred to as a device transmission. The receiving device (e.g., anRFID reader) is referenced as a detector which could be an RFID antenna.

Referring now to FIGS. 1-2, there are provided schematic illustrationsof an exemplary passage 100 that is useful for understanding the presentinvention. The present invention is described herein in relation to aretail store environment. The present invention is not limited in thisregard, and can be used in other environments. For example, the presentinvention can be used in distribution centers, factories and othercommercial environments. Notably, the present invention can be employedin any environment in which objects, items or persons need to be locatedand/or tracked. The present invention can also be employed in anyenvironment in which a person is to be provided restricted access to agiven area.

The passage 100 comprises a point at which a person can transition fromone area (e.g., an external area 304) to another area (an internal area302). Each area comprises an open space that is virtually or physicallydemarcated. For example, the passage 100 allows a person to enter andexit a retail store facility 300. In this scenario, the passage 100 mayinclude a door. The passage 100 is sub-divided into a plurality of zones1-6. Six zones are shown in FIG. 2. The present invention is not limitedin this regard. Any number of zones can be employed in accordance with aparticular application (e.g., 2 zones, 4 zones or 10 zones). Each zonehas one or more RSSI profiles associated therewith which were createdfor all or some of the possible orientations of the tag 310. ExemplaryRSSI profiles will be discussed below in relation to TABLE 1.

Prior to discussing TABLE 1, it should be understood that at least onedetector 202-216 is disposed on or adjacent to a portion of the passage100 defining a respective zone 1, 2, 3, 4, 5 or 6. Each detector 202-216is configured to transmit signals to and receive signals from tags 310located in proximity thereto. In some scenarios, at least one tagcomprises a Common Access Card (“CAC”), employee badge, security tag, acellular phone, an ID beacon or other signal transmitting device. Thetags 310 include, but are not limited to, RFID enabled tags or Bluetoothenabled tags having dipole antennas. Accordingly, each detectorincludes, but is not limited to, an RFID reader, an RF beacon, or aBluetooth enabled device.

During operation, the tag 310 periodically transmits a wireless signal(or device transmission) which is received by all or some of thedetectors 202-216. The periodic transmissions can be performed inresponse to an interrogation signal received at the tag or alternativelyautomatically in accordance with pre-defined timing criteria. The RSSIfor each received wireless signal is determined by the respectivedetector. Thereafter, the relationship of the RSSIs is used by acomputing device 218 in a subsequent process to estimate a location ofthe tag 310. More specifically, the computing device 218 determines: (1)whether the tag 310 is located in a passage 100; (2) in which zone 1, 2,3, 4, 5 or 6 of the passage 100 is the tag located; (3) whether the tag310 is located inside or outside of the retail store facility 300;and/or (4) in which internal (or inside) area 302 or external (oroutside) area 304 is the tag 310 located.

Only one internal area and only one external area are shown in FIG. 3.The present invention is not limited in this regard. For example, aplurality of detectors can be employed so as to facilitate thedetermination as to which one of a plurality of internal or externalareas a given tag is located in.

Referring now to TABLE 1, a plurality of exemplary RSSI profiles areshown.

TABLE 1 Zone 2-RSSI Zone 2-RSSI Zone 3-RSSI Profile-VerticalProfile-Diagonal Profile-Vertical Tag Right Tag Tag RSSI Profile-Orientation Orientation Orientation Distant Tag RSSI (dBm) Ratio RSSI(dBm) Ratio RSSI (dBm) Ratio RSSI (dbm) Ratio Detector 202 −60 0.66 −740.00 −85 0.00 −75 0.67 Number 204 −50 1.00 −52 1.00 −62 0.70 −79 1.00206 −60 0.66 −57 0.77 −52 1.00 −81 0.67 208 −79 0.00 −67 0.32 −81 0.12−89 0.33 Standard 12.12 9.88 15.64 5.89 Deviation Range 29 22 33 14As evident from TABLE 1, each zone is identified by the respective RSSIprofile defined by characteristics of the wireless signal received atthe detectors. For example, the RSSI values at the detectors areevaluated to determine the relationship therebetween. The term “RSSIvalue”, as used herein, refers to the average of at least two samplescollected over a (possibly very brief) period of time (e.g., 50microseconds to perhaps 1 millisecond, roughly). The average may be over2-4 samples or even dozens of samples in that time period. The idea isto average out random variation in the RF environment and small circuitnoise in the device, without averaging over such a large period of timethat the average starts to include RSSI differences due to changes inlocation of the tag itself. Based on the determined RSSI values andrelationships therebetween, the computing device 218 can derive anestimate of a zone location where the wireless transmission originated.Additionally, the determined RSSI values can be correlated to theorientation of the tag.

In some scenarios, the RSSI values are normalized and used by thecomputing device 218 in a ratio or relational analysis. For example,TABLE 1 defines possible RSSI profile relations for detectors 202, 204,206 and 208. When the tag 310 is in a zone, the RSSI values are capturedand the relational RSSI ratios for the detectors are estimated. Therelational RSSI ratios were computed in Excel as follows.

Ratio=(RSSI_(X)−RSSI_(smallest))/Range

where Ratio represents the relational RSSI ratio, RSSI_(X) representsthe RSSI value for the respective detector, RSSI_(smallest) representsthe smallest RSSI value of a set of RSSI values, and Range representsthe range. As such, the relational RSSI ratios for “Zone 2-RSSIProfile-Vertical Orientation” are computed as follows:((−60)-(−79))/29=0.66; ((−50)-(−79))/29=1.00; ((−60)-(−79))/29=0.66; and((−79)-(−79))/29=0.00. Similarly, the ranges for “Zone 2-RSSIProfile-Diagonal Right Tag Orientation” are computed as follows:((−74)-(−74))/22=0.00; ((−52)-(−74))/22=1.00; ((−57)-(−74))/22=0.77; and((−67)-(−74))/22=0.32. The ranges for “Zone 3-RSSI Profile-Vertical TagOrientation” are computed as follows: ((−85)-(−85))/33=0.00;((−62)-(−85))/33=0.70; ((−52)-(−85))/33=1.00; and ((−81)-(−85))/33=0.12.The ranges for “RSSI Profile-Distant Tag” are computed in the same way.On a distant tag, differences in results among zones diminish as thedistance increases. In other words, if the distant tag is 30 or 40 feetaway, the ratios computed for zone 2 and 3 should start to look similar.This must be the case since, in the limit of very large distance, thedistance between zones is negligible compared to the distance betweenthe tag and any one zone. The zones become mathematically indistinctfrom one another for increasingly large tag separation.

TABLE 1 also includes possible detection profiles when the tag 310 is ina plurality of orientations. The RSSI value of one detector couldprovide an indication of tag rotation relative to the other detectors.Distant tags may also be discriminated based on standard deviation ofthe detected RSSI values. The standard deviation is quantitativelysmaller for distant tags than for a tag in the passage 100. The standarddeviation is computed in Excel as follows.

SD=STDEV(RSSI₂₀₂:RSSI₂₀₈)

where SD represents the standard deviation, RSSI₂₀₂ represents the RSSIvalue for detector 202, and RSSI₂₀₈ represents the RSSI value fordetector 208. In Excel, the STDEV function measures how widely values ina set differ from the average, or mean, value. The mathematicaloperations implemented by the STDEV function are outlined below for the“Zone 2-RSSI Profile-Vertical Orientation”.

-   -   Calculate the average, or mean        value=(−60)+(−50)+(−60)+(−79)=−249/4=−62.25    -   Calculate deviations of RSSI dBm data points from the average or        mean value, square the results of each, and divide the results        of each by (n-1), where n is the number of values.

((−60)-(−62.25))²=(2.25)²=5.0625/3=1.69

(−50-−62.25)²=(12.25)²=150.0625/3=50.02

(−60-−62.25)²=(2.25)²=5.0625/3=1/69

(−79-−62.25)²=(−16.75)²=280.5625/3=93.52

-   -   Take the square root of the sum of the results to obtain the        standard-deviation.

√(1.69+50.02+1.69+93.52)=√146.92=12.12

The standard deviations for the other RSSI profiles of TABLE 1 can becomputed in a similar manner.

The range values of TABLE 1 can be computed as follows in Excel.

Range=MAX(RSSI₂₀₂:RSSI₂₀₈)−MIN(RSSI₂₀₂:RSSI₂₀₈)

where Range represents the range value, RSSI₂₀₂ represents the RSSIvalue for detector 202, and RSSI₂₀₈ represents the RSSI value fordetector 208. In Excel, the MAX function finds the maximum value in arange of cells. The MIN function finds the minimum value in a range ofcells. Accordingly, the range for “Zone 2-RSSI Profile-VerticalOrientation” is computed as follows: −79-−50=29. Similarly, the rangefor “Zone 2-RSSI Profile, Diagonal Right Tag Orientation” is computed asfollows: −74-−52=22. The range for “Zone 3-RSSI Profile-Vertical TagOrientation” is computed as follows: −85-−52=33. The range for “RSSIProfile-Distant Tag” is computed as follows: −89-−75=14.

In some scenarios specified in TABLE 1, a tag 310 transmits a wirelesssignal that is received by detectors 202, 204, 206 and 208. Thedetectors respectively process the received signals to determine theRSSI values thereof. The RSSI values are then used to determine aprobability that the tag 310 is located within one of the zones 1-6. Forexample, if the RSSI values associated with detector 202 is −60 dBm,detector 204 is −50 dBm, detector 206 is −60 dBm and detector 208 is −79dBm, then a determination is made that the tag 310 has a vertical tagorientation and is probably located in zone 2 of the passage 100.Additionally or alternatively, if a standard deviation of the RSSIvalues is approximately 12.12 and/or range is approximately 29, then adetermination is made that the tag 310 has a vertical tag orientationand is probably located in zone 2 of the passage 100. In contrast, ifthe RSSI values associated with detector 202 is −75 dBm, detector 204 is−79 dBm, detector 206 is −81 dBm and detector 208 is −89 dBm, then adetermination is made that the tag 310 is probably not located in any ofthe zones 1-6 because it is located relatively far from the passage 100(e.g., in an external area 304). Additionally or alternatively, if astandard deviation of the RSSI values is approximately 5.89 and/or rangeis approximately 14, then a determination is made that the tag 310 isprobably not located in any of the zones 1-6 because it is locatedrelatively far from the passage 100 (e.g., in an external area 304).

Notably, the technique employed herein to define a tracking anddetection architecture uses the combination of passage and areainformation for determining an outcome of detection in the passage 100.The outcome of passage and area likelihood outcomes are communicated toa decision engine of the computing device 218 based on well-knownstatistical detection concepts. A schematic illustration is provided inFIG. 4 that is useful for understanding how the decision engine derivesits output in some scenarios.

As shown in FIG. 4, the passage algorithm employed by the computingdevice 218 comprises the performance of a plurality of operations. Theoperations include passage RSSI based operations. The inputs for thepassage algorithm are provided by the detectors 202-216 disposed on oradjacent to the passage 100 and zones 1-6. For example, RSSIs ofwireless signals transmitted from the tag 310 and received at thedetectors 202-216 are provided to the computing device 218 for use inthe previously listed operations.

The passage RSSI operations begin with functional block 402 in whichRSSI values are processed to identify a possible zone that the tag 310is located in, as well as determine a confidence value for the probablezone. The zone predication is made using RSSI profiles as describedabove in relation to TABLE 1. The confidence value is determined by thedifference between the measured statistical data and the expectedstatistical data for a zone. The degree to which the expected andmeasured statistical data match would define the confidence orlikelihood of a correct decision.

The outputs of functional block 402 are passed to functional block 403.In functional block 403, a likelihood value is determined. Thelikelihood value indicates the probability that the probable zone valueis correct. The probable zone and likelihood value are than passed tofunctional block 410. In functional block 410, a determination is madeas to whether or not the likelihood value meets a pre-specified criteria(e.g., exceeds a threshold value). If the likelihood value meets thepre-specified criteria, then the probable area is passed to functionalblock 412, which will be described below.

As also shown by FIG. 4, the area algorithm employed by the computingdevice 218 comprises the performance of a plurality of operations. Theoperations include passage RSSI based operations. The inputs for thearea algorithm are provided by the detectors 306 disposed in internalareas 302 of the retail store facility 300 and detectors 308 disposed inareas 304 external to the retail store facility 300. For example, RSSIsof wireless signals transmitted from the tag 310 and received at thedetectors 306, 308 are provided to the computing device 218 for use inthe previously listed operations.

The passage RSSI based operations are performed in functional block 406.The operations of functional block 406 is the same as or similar tothose performed in functional blocks 402. As such, the descriptionprovided above in relation to functional block 402 is sufficient forunderstanding the operations performed in functional blocks 406.

The outputs of functional block 406 are passed to functional block 408.In functional block 408, a likelihood value is determined. Thelikelihood value indicates the probability that the probable area valueis correct. The probable area and likelihood value are than passed tofunctional block 410. In functional block 410, a determination is madeas to whether or not the likelihood value meets a pre-specified criteria(e.g., exceeds a threshold value). If the likelihood value meets thepre-specified criteria, then the probable area is passed to functionalblock 412 for use in generating an estimated area output. The output offunctional block 412 indicates (1) the probable location of the tag 310in relation to a passage zone, and/or (2) in what area of the store isthe tag's most probable location.

Referring now to FIG. 5, there is provided a block diagram of anexemplary architecture for a detector 500. Detectors 202-216, 306 and308 are the same as or similar to the detector 500. As such, thediscussion of detector 500 is sufficient for understanding detectors202-216, 306 and 308.

Detector 500 may include more or less components that that shown in FIG.5. However, the components shown are sufficient to disclose anillustrative embodiment implementing the present invention. Some or allof the components of the detector 500 can be implemented in hardware,software and/or a combination of hardware and software. The hardwareincludes, but is not limited to, one or more electronic circuits. Theelectronic circuit may comprise passive components (e.g., capacitors andresistors) and active components (e.g., processors) arranged and/orprogrammed to implement the methods disclosed herein.

The hardware architecture of FIG. 5 represents an embodiment of arepresentative detector 500 configured to facilitate improved taglocation estimations. In this regard, the detector 500 comprises an RFenabled device 550 for allowing data to be exchanged with an externaldevice (e.g., tag 310 of FIG. 1) via RF technology. The components504-516 shown in FIG. 5 may be collectively referred to herein as the RFenabled device 550, and include a power source 512 (e.g., a battery).

The RF enabled device 550 comprises an antenna 502 for allowing data tobe exchanged with the external device via RF technology (e.g., RFIDtechnology or other RF based technology). The external device maycomprise a tag 310 of FIG. 3. In the case that the tag 310 is an RFIDtag, the antenna 302 is configured to transmit RF carrier signals (e.g.,interrogation signals) to the tag 310, and/or receive data responsesignals (e.g., authentication reply signals) generated by the tag 310.In this regard, the RF enabled device 550 comprises an RF transceiver508. RFID transceivers are well known in the art, and therefore will notbe described herein. However, it should be understood that the RFtransceiver 508 receives RF signals including information from thetransmitting device, and forwards the same to a logic controller 510 forextracting the information therefrom.

Notably, memory 504 may be a volatile memory and/or a non-volatilememory. For example, the memory 504 can include, but is not limited to,a Random Access Memory (“RAM”), a Dynamic Random Access Memory (“DRAM”),a Static Random Access Memory (“SRAM”), a Read-Only Memory (“ROM”)and/or a flash memory. The memory 504 may also comprise unsecure memoryand/or secure memory. The phrase “unsecure memory”, as used herein,refers to memory configured to store data in a plain text form. Thephrase “secure memory”, as used herein, refers to memory configured tostore data in an encrypted form and/or memory having or being disposedin a secure or tamper-proof enclosure.

Instructions 522 are stored in memory for execution by the RF enableddevice 550 and that cause the RF enabled device 550 to perform any oneor more of the methodologies of the present disclosure. The instructions522 are generally operative to facilitate determinations as to wheretags are located within a facility, passage or external area. Otherfunctions of the RF enabled device 550 should be apparent from the abovediscussion.

It should also be noted that the system shown in FIG. 5 can incorporateWake-On-Radio (“WOR”) enabled transceiver technology. In this case,large parts of the transceiver 508 and logic controller 510 may begenerally placed in deep sleep mode to conserve power. When thetransceiver receives an approaching tag, or alternatively a wake-upmessage from another motion sensing device in the area equipped with acompatible transceiver, the detector components (508 and 510specifically) transition to full power mode for execution of thelocation determining processes described herein.

Note that in some cases, the battery 512 may be replaced with a powersupply which is connected to mains power or interface 582 (e.g., powerover Ethernet), or in some cases may even be replaced with energyharvesting circuitry including a transducer and charge storage, such asa super-capacitor.

Referring now to FIG. 6, there is provided a detailed block diagram ofan exemplary architecture for a computing device 600. Computing device218 of FIG. 2 is the same as or substantially similar to computingdevice 600. As such, the following discussion of computing device 600 issufficient for understanding computing device 218.

Notably, the computing device 600 may include more or less componentsthan those shown in FIG. 6. However, the components shown are sufficientto disclose an illustrative embodiment implementing the presentinvention. The hardware architecture of FIG. 6 represents one embodimentof a representative computer device configured to facilitate (a) thedetermination of locations of tags within a facility, passage orexternal area and/or (b) the provision of a three dimensional mapshowing the location of a tag. As such, the computing device 600 of FIG.6 implements at least a portion of a method for providing such taglocations in accordance with embodiments of the present invention.

Some or all the components of the computing device 600 can beimplemented as hardware, software and/or a combination of hardware andsoftware. The hardware includes, but is not limited to, one or moreelectronic circuits. The electronic circuits can include, but are notlimited to, passive components (e.g., resistors and capacitors) and/oractive components (e.g., amplifiers and/or microprocessors). The passiveand/or active components can be adapted to, arranged to and/orprogrammed to perform one or more of the methodologies, procedures, orfunctions described herein.

As shown in FIG. 6, the computing device 600 comprises a user interface602, a Central Processing Unit (“CPU”) 606, a system bus 610, a memory612 connected to and accessible by other portions of computing device600 through system bus 610, and hardware entities 614 connected tosystem bus 610. The user interface can include input devices (e.g., akeypad 650) and output devices (e.g., speaker 652, a display 654, and/orlight emitting diodes 656), which facilitate user-software interactionsfor controlling operations of the computing device 600. Also, maps maybe presented to the user of the computing device 600 via the display654. The maps may include a three dimensional map showing the estimatedlocations of the tags within a virtual area, and/or a heat map overlaidon an image inventory space showing the uncertainty of tag locations.

At least some of the hardware entities 614 perform actions involvingaccess to and use of memory 612, which can be a Random Access Memory(“RAM”), a disk driver and/or a Compact Disc Read Only Memory(“CD-ROM”). Hardware entities 614 can include a disk drive unit 616comprising a computer-readable storage medium 618 on which is stored oneor more sets of instructions 620 (e.g., software code) configured toimplement one or more of the methodologies, procedures, or functionsdescribed herein. The instructions 620 can also reside, completely or atleast partially, within the memory 612 and/or within the CPU 606 duringexecution thereof by the computing device 600. The memory 612 and theCPU 606 also can constitute machine-readable media. The term“machine-readable media”, as used here, refers to a single medium ormultiple media (e.g., a centralized or distributed database, and/orassociated caches and servers) that store the one or more sets ofinstructions 620. The term “machine-readable media”, as used here, alsorefers to any medium that is capable of storing, encoding or carrying aset of instructions 620 for execution by the computing device 600 andthat cause the computing device 600 to perform any one or more of themethodologies of the present disclosure.

In some embodiments of the present invention, the hardware entities 614include an electronic circuit (e.g., a processor) programmed forfacilitating (a) determinations of locations of tags within a passage orarea and/or (b) the provision of a three dimensional map showinglocations of tags within the passage or area. In this regard, it shouldbe understood that the electronic circuit can access and run softwareapplications 624 installed on the computing device 600. The softwareapplication 624 is generally operative to facilitate: the determinationof tag locations within a passage or area; and the mapping of the taglocations in a virtual three dimensional space. Other functions of thesoftware application 624 should be apparent from the above discussion.

All of the apparatus, methods, and algorithms disclosed and claimedherein can be made and executed without undue experimentation in lightof the present disclosure. While the invention has been described interms of preferred embodiments, it will be apparent to those havingordinary skill in the art that variations may be applied to theapparatus, methods and sequence of steps of the method without departingfrom the concept, spirit and scope of the invention. More specifically,it will be apparent that certain components may be added to, combinedwith, or substituted for the components described herein while the sameor similar results would be achieved. All such similar substitutes andmodifications apparent to those having ordinary skill in the art aredeemed to be within the spirit, scope and concept of the invention asdefined.

The features and functions disclosed above, as well as alternatives, maybe combined into many other different systems or applications. Variouspresently unforeseen or unanticipated alternatives, modifications,variations or improvements may be made by those skilled in the art, eachof which is also intended to be encompassed by the disclosedembodiments.

We claim:
 1. A method for determining a location of a tag, comprising:receiving, at each detector of at least one of a plurality of firstdetectors and a plurality of second detectors, a device transmissionperiodically transmitted from the tag, where the plurality of firstdetectors are disposed in proximity to a passage at which a person cantransition from a first demarcated area to a second demarcated area, theplurality of second detectors are disposed within the first and seconddemarcated areas, and the passage is sub-divided into a plurality ofzones; determining, by at least one of the plurality of first detectorsand the plurality of second detectors, Received Signal StrengthIndictors (“RSSIs”) for the device transmission received thereat;determining, by a computing device, a probable location of the tagwithin the passage, first demarcated area or second demarcated areausing the RSSIs and relationships between the RSSIs; determining a firstlikelihood value indicating the likelihood that the probable location iscorrect; and determining an estimated location of the tag within thepassage, first demarcated area or second demarcated area based on theprobable location when the first likelihood value meets a firstcriteria.
 2. The method according to claim 1, wherein the estimatedlocation comprises a zone selected from the plurality of zones where thedevice transmission originated.
 3. The method according to claim 1,wherein the zone is selected based on relational RSSI ratios computedusing the RSSIs determined by the plurality of first detectors.
 4. Themethod according to claim 1, wherein the first likelihood value isdetermined based on a confidence value computed for the probablelocation.
 5. The method according to claim 4, wherein the confidencevalue is computed based on a statistical analysis and RSSI ratiocalculations for RSSI levels received by the plurality of firstdetectors.
 6. The method according to claim 4, wherein the confidencevalue is assigned based on how well correlated measured statisticalvalues are to reference statistical values.
 7. A system, comprising: atag; a plurality of first detectors and a plurality of second detectors,the plurality of first detectors disposed in proximity to a passage atwhich a person can transition from a first demarcated area to a seconddemarcated area, the plurality of second detectors disposed within thefirst and second demarcated areas, and the passage sub-divided into aplurality of zones, where each detector of the plurality of first andsecond detectors is configured to receive a device transmissionperiodically transmitted from the tag, and determine a Received SignalStrength Indictors (“RSSI”) for the device transmission receivedthereat; and an electronic circuit communicatively coupled to theplurality of first and second detectors, and configured to determine aprobable location of the tag within the passage, first demarcated areaor second demarcated area using the RSSIs and relationships between theRSSIs, determine a first likelihood value indicating the likelihood thatthe probable location is correct, and determine an estimated location ofthe tag within the passage, first demarcated area or second demarcatedarea based on the probable location when the first likelihood valuemeets a first criteria.
 8. The system according to claim 7, wherein theestimated location comprises a zone selected from the plurality of zoneswhere the device transmission originated.
 9. The system according toclaim 7, wherein the zone is selected based on relational RSSI ratioscomputed using the RSSIs determined by the plurality of first detectors.10. The system according to claim 7, wherein the first likelihood valueis determined based on a confidence value computed for the probablelocation.
 11. The system according to claim 10, wherein the confidencevalue is computed based on a statistical analysis and RSSI ratiocalculations for RSSI levels received by the plurality of firstdetectors.
 12. The system according to claim 10, wherein the confidencevalue is assigned based on how well correlated measured statisticalvalues are to reference statistical values.